Particles and Textures and Density
If I understand you correctly (and I might not) and you want to control particle emission with an image sequence, then this isn't possible. Only the first image in an image sequence will be taken into account for particle density.

According to Brecht, one of the Blender developers here:


  The problem here is a limitation of the particle system. The way it works is that a distribution of particles is generated once beforehand (to have an even distribution), and can't be dynamically changed.